Silicon carbide thermostable porous structural material and process for producing the same

ABSTRACT

After a slurry containing powdered silicon and a resin used as a carbon source is applied by impregnation to a carbon powder-made porous structural body having a bone structure, which is formed from powdered carbon, and is then carbonized at 900 to 1,300° C. in a vacuum or an inert gas atmosphere, reaction sintering is performed at a temperature of 1,300° C. or more in a vacuum or an inert gas atmosphere. Accordingly, since a carbonized porous structural body can be obtained which has open pores generated by a volume-reduction reaction at the same time when porous silicon carbide having a good wettability to molten silicon is formed, this carbonized porous structural body is impregnated with molten silicon at a temperature of 1,300 to 1,800° C. in a vacuum or an inert gas atmosphere.

TECHNICAL FIELD

The present invention relates to silicon carbide-based heat-resistanceporous structural materials and manufacturing methods thereof, eachmaterial formed using a carbon powder-made porous structural body bytwo-stage reaction sintering performed in combination of reactionsintering between silicon and carbon and melt impregnation of silicon orsimply by melt impregnation of silicon, the carbon powder-made porousstructural body having a honeycomb shape or the like and being formedfrom powdered carbon. In more particular, the present invention relatesto a silicon carbide-based heat-resistance porous structural materialand a manufacturing method thereof, the structural material being usedin many applications such as a high temperature structural member, aheat exchanger, a high temperature catalyst carrier, a high temperaturefilter, a filter medium for molten metal, and a furnace member.

BACKGROUND ART

Since being light weight and having superior heat resistance, abrasionresistance, corrosion resistance, and the like, in recent years, asilicon carbide-based ceramic has been widely used in various fields,such as a high-temperature and corrosion resistant member, a heatermaterial, a heat exchanger, and an abrasion resistant member, and hasalso been further used as abrasives, grinding stones, and the like.Since this silicon carbide is primarily manufactured by a sinteringtechnique, a sintering auxiliary agent is required, and since being usedin the form of a dense bulk material, as of today, the silicon carbidehas not been practically used as a filter having a complicated shape anda light-weight porous structural material having a honeycomb shape orthe like.

Although a silicon carbide-based ceramic having a honeycomb shape hasbeen formed by extrusion molding, there have been problems in that amolding machine and a mold thereof are expensive and that the shape isdetermined by the mold.

In addition, since an auxiliary agent is used, the heat resistance isinferior, and large dimensional shrinkage occurs by sintering.

In addition, a method for forming a silicon carbide-based ceramic havinga honeycomb shape has been disclosed in Japanese Unexamined PatentApplication Publication No. 2001-226174 in which a paper-made corrugatedfiberboard is impregnated with a slurry containing a resin and powderedsilicon and is then carbonized, followed by reaction sintering and meltimpregnation of silicon; however, since the paper-made corrugatedfiberboard has a dimensional shrinkage of 10% to 20% in firing, and thesurface thereof does not become a flat surface but it undulates.Furthermore, since a remaining carbon amount of the paper isapproximately only 10 percent by weight of the weight of the corrugatedfiberboard, and a carbon yield obtained from the resin is also up to 60percent by weight, the amount of carbon is small, and hence the amountof silicon carbide to be obtained by reaction with silicon is alsosmall, thereby causing a problem in that the strength thereof is nothigh as a structural material. In addition, since the paper-madecorrugated fiberboard is formed from waste paper as a starting material,calcium carbonate and oxides such as titanium oxide are contained in anamount of approximately 10 percent by weight of the weight of thecorrugated fiberboard, and the oxides mentioned above serve asimpurities and degrade heat resistance properties of the ceramic used asa structural material.

Through research on a fiber-reinforced silicon carbide compositematerial, the inventor of the present invention found that reaction offorming silicon carbide, which reaction is between powdered silicon andcarbon obtained from a resin, occurs while causing a decrease in volume,and that adhesion to a fiber is superior (Japanese Patent No. 2045825).In addition, it was also found that when a porous material such as acorrugated fiberboard or sponge is impregnated with a slurry formed of aphenol resin and powdered silicon and is then processed by reactionsintering, followed by melt impregnation of silicon, a siliconcarbide-based heat-resistance, light-weight, porous structural materialcan be manufactured in which bone portions are dense and have a smallspecific surface area (Japanese Unexamined Patent ApplicationPublication No. 2001-226174).

Based on the findings described above, the present invention provides asilicon carbide-based heat-resistance porous structural material formedby an inexpensive process and a manufacturing method thereof, in whichvarious shortcomings of a conventional silicon carbide-based porousstructural material and a manufacturing method thereof are overcome, theshape of an as-molded porous structural body having a bone structure canbe maintained without substantial shrinkage, the bone structure is denseand strong, and a product can be easily formed therefrom even when ithas a complicated shape.

That is, through intensive research carried out by the inventor of thepresent invention on the silicon carbide-based heat-resistance,light-weight, porous structural material, the following were confirmed.That is, when a mixed slurry formed of powdered silicon and a resin isapplied by impregnation to a bone structure of a carbon powder-madeporous structural body, such as a corrugated fiberboard shape, followedby firing in a vacuum or an inert gas atmosphere, a strength maintainingthe shape is obtained even after carbonization performed at 1,000° C.,the dimensional shrinkage is very small, such as approximately 3%, andat a temperature of 1,300° C. or more, by reaction forming siliconcarbide between the powdered silicon and carbon obtained from the resin,which causes the decrease in volume, porous silicon carbide can beformed on the surface.

In addition, it was found that, in melt impregnation of silicon at amelting point of silicon or more, this porous silicon carbide has a goodwettability to molten silicon and is likely to react therewith and alsowith the carbon powder-made porous structural body present inside so asto form dense silicon carbide; hence, the present invention was finallymade. Furthermore, it was also confirmed that when a resin slurry isapplied by impregnation to a carbon powder-made porous structural bodyhaving a bone structure and is then carbonized, followed by meltimpregnation of silicon, dense silicon carbide can be formed.

DISCLOSURE OF INVENTION

A first silicon carbide-based heat-resistance porous structural materialof the present invention, which is formed based on the descriptiondescribed above, is produced by a process comprising the step ofimpregnating a carbonized porous structural body with molten silicon,the structural body having open pores open to a surface thereof whichare generated due to a volume-reduction reaction and at the same timecontaining porous silicon carbide which has a good wettability to moltensilicon. In addition, the carbonized porous structural body is formed bythe steps of applying a slurry by impregnation to a carbon powder-madeporous structural body having a bone structure, which is formed frompowdered carbon, and then carbonizing the slurry, followed by reactionsintering, the slurry containing powdered silicon and a resin used as acarbon source.

In addition, a second silicon carbide-based heat-resistance porousstructural material of the present invention is produced by a processcomprising the step of impregnating a carbonized porous structural bodywith molten silicon, the structural body having carbon on a surfacethereof generated from a resin by carbonization so as to maintain theoriginal shape after carbonization and at the same time containingpowdered carbon having a good wettability to molten silicon. Inaddition, the carbonized porous structural body is formed by the stepsof applying a slurry by impregnation to a carbon powder-made porousstructural body having a bone structure, which is formed from powderedcarbon, and then carbonizing the slurry.

As the carbon powder-made porous structural body having a bonestructure, in general, a carbon product having a honeycomb, a corrugatedfiberboard, or a cardboard shape is used which is formed by adding abinding agent to the powdered carbon, followed by molding.

In more particular, the silicon carbide-based heat-resistance porousstructural material of the present invention is formed by the steps ofcovering the carbon powder-made porous structural body having a bonestructure with a resin so as to maintain the shape after carbonization,mixing powdered silicon into the resin whenever necessary, then formingsilicon carbide having a good wettability to molten silicon by reactionsintering and open pores in surface portions of the bone structureresulting from a volume-reduction reaction, the silicon carbide beingformed between powdered silicon and amorphous carbon obtained from theresin, and performing melt impregnation of silicon.

When the amorphous carbon obtained by carbonizing the resin is dense,molten silicon hardly reacts therewith. However, since the carbonpowder-made porous structural body is composed of porous carbon which isreactive with molten silicon, without mixing powdered silicon with theresin for reaction sintering, when the amount of amorphous carbonobtained from the resin is small, melt impregnation of silicon can beperformed. In addition, since the bone structure of the carbonpowder-made porous structural body is formed of carbon, the shrinkagethereof after firing is hardly observed, and furthermore, since the bonestructure is formed from carbon itself instead of paper having a lowcarbon yield, the amount of silicon carbide obtained by the reactionbetween carbon and silicon is large, thereby obtaining a high strength.

In addition, a method for manufacturing the above first siliconcarbide-based heat-resistance porous structural material, of the presentinvention, comprises the steps of: applying a slurry containing powderedsilicon and a resin used as a carbon source by impregnation to a carbonpowder-made porous structural body having a bone structure, which isformed from powdered carbon, then carbonizing the slurry at 900 to1,300° C. in a vacuum or an inert gas atmosphere, then performingreaction sintering at a temperature of 1,300° C. or more in a vacuum oran inert gas atmosphere so as to form a carbonized porous structuralbody having open pores which are generated by a volume-reductionreaction at the same time when porous silicon carbide having a goodwettability to molten silicon is formed, and impregnating thiscarbonized porous structural body with silicon at a temperature of 1,300to 1,800° C. in a vacuum or an inert gas atmosphere.

Furthermore, a method for manufacturing the above second siliconcarbide-based heat-resistance porous structural material, of the presentinvention, comprises the steps of: applying a slurry containing a resinused as a carbon source by impregnation to a carbon powder-made porousstructural body having a bone structure, which is formed from powderedcarbon, then carbonizing the slurry at 900 to 1,300° C. in a vacuum oran inert gas atmosphere so as to form a carbonized porous structuralbody having carbon generated on a surface thereof from the resin and atthe same time containing powdered carbon having a good wettability tomolten silicon, and impregnating this carbonized porous structural bodywith silicon at a temperature of 1,300 to 1,800° C. in a vacuum or aninert gas atmosphere.

According to the methods of the present invention as described above, alarge structural body having a complicated shape can be easily formed,and when the porous structure body is machined after carbonization,machining can be easily performed since the porous structure body has astrength capable of withstanding the machining.

As the carbon powder-made porous structural body having a bonestructure, used in the methods described above, a structural bodycapable of holding the slurry on the surface thereof is preferable, andin particular, a carbon product is suitably used which is formed byextrusion of powdered carbon added with a binding agent into a honeycombshape or by paper making of powdered carbon added with a binding agentinto a corrugated fiberboard or a cardboard shape.

In addition, as the resin used as a carbon source in the methodsdescribed above, which is applied by impregnation to the bone structureof the porous structural body, a phenol resin, a furan resin, apolycarboxysilane, an organic metal polymer, and pitch may be preferablymentioned. The resins mentioned above may be used alone or incombination.

Furthermore, as an additive added to the slurry with which the bonestructure of the carbon powder-made porous structural body isimpregnated, at least one selected from the group consisting of powderedcarbon, powdered graphite, and carbon black may be added, and as anaggregate or an antioxidant, at least one selected from the groupconsisting of silicon carbide, silicon nitride, titania, zirconia,zircon, alumina, silica, mullite, molybdenum disilicide, boron carbide,boron, and powdered silicon may be added.

As the powdered silicon contained in the slurry or the silicon for meltimpregnation, used in the methods described above, a silicon alloycontaining at least one element selected from the group consisting ofmagnesium, aluminum, titanium, chromium, manganese, iron, cobalt,nickel, copper, zinc, zirconium, niobium, molybdenum, and tungsten, or amixture of the above element and powdered silicon may be used.

According to the silicon carbide-based heat-resistance porous structuralmaterial of the present invention and the manufacturing method thereof,a silicon carbide-based heat-resistance, light-weight, porous compositematerial can be easily formed while the original shape of a porousstructural body is maintained, and in addition, since a complicatedshape can also be easily formed, the composite material described abovecan be used in wide and various applications such as a high temperaturefilter, a high temperature structural member, a heat insulatingmaterial, a filter medium for molten metal, a burner plate, a heatermaterial, and a high temperature sound absorber.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, preferable embodiments of the methods according to the presentinvention will be described.

When a first silicon carbide-based heat-resistance porous structuralmaterial of the present invention is manufactured, a slurry, which isformed by mixing a dissolved phenol resin used as a carbon source andpowdered silicon, is sufficiently applied to a carbon powder-made porousstructural body having a bone structure, or a carbon powder-made porousstructural body is immersed in the slurry described above forimpregnation, and subsequently, drying is performed.

In addition, when a second silicon carbide-based heat-resistance porousstructural material is manufactured, a slurry containing a phenol resinor the like used as a carbon source is sufficiently applied to a carbonpowder-made porous structural body having a bone structure byimpregnation as is the case described above, followed by drying.

The drying in both cases described above is desirably performed atapproximately 70° C. for about 12 hours.

As the above carbon powder-made porous structural body having a bonestructure, as described above, a carbon product which is formed byextrusion of powdered carbon added with a binding agent into a honeycombshape or by paper making of powdered carbon added with a binding agentinto a corrugated fiberboard or a cardboard shape may be used as it isor may be formed into an optional shape using an adhesive or the likefor the use.

In addition, as the resin with which the bone structure of the porousstructural body is impregnated, at least one of a resin selected fromthe group consisting of a phenol resin, a furan resin, apolycarboxysilane, an organic metal polymer, and pitch may be used, andwhenever necessary, the above additive and the like may also be added.

Furthermore, as the powdered silicon used for forming silicon carbide, afine powder is suitably used, and in particular, a fine powder having anaverage particle size of 30 μm or less is suitably used. A powder havinga larger particle diameter may be formed into a fine powder bypulverization using a ball mill or the like.

Next, the carbon powder-made porous structural body thus formed iscarbonized in a vacuum or an inert gas atmosphere at a temperature ofapproximately 900 to 1,300° C. When powdered silicon is added to theslurry for forming the first silicon carbide-based heat-resistanceporous structural material, a carbonized porous structural body obtainedthereby has a bone portion made of powdered carbon and a mixed portionpresent on the surface of the carbon powder-made bone portion so as tocover it, the mixed portion being composed of the powdered silicon andamorphous carbon formed by carbonization of the phenol resin.

Subsequently, in both cases in which the first and the second porousstructural materials are manufactured, the shape of the bone structureis not deformed or shrunk, and the original shape thereof can besubstantially maintained. In addition, the carbonized porous structuralbody has a strength capable of withstanding machining.

When powdered silicon is added to the slurry described above, thiscarbonized porous structural body is processed by firing treatment in avacuum or an inert gas atmosphere at a temperature of approximately1,300 to 1,420° C. after carbonization so that amorphous carbon obtainedfrom the phenol resin and the silicon are allowed to react with eachother, thereby forming porous silicon carbide on the bone structure.Accordingly, at the same time when porous silicon carbide having a goodwettability to molten silicon is formed, since this reaction is avolume-reduction reaction, open pores open to the surface are formed bythis volume-reduction reaction. As a result, a porous structural bodymade of silicon carbide having pores can be obtained.

Next, this carbonized porous structural body is impregnated with moltensilicon in a vacuum or an inert gas atmosphere at a temperature of 1,300to 1,800° C., thereby obtaining the silicon carbide-basedheat-resistance porous structural material of the present invention.

In addition, the ratio of the powdered silicon to the resin used in theabove method of the present invention is preferably set so that theratio Si/C of silicon to carbon on an atomic basis is in the range of 0to 5.

As described above, without mixing powdered silicon with the resin ofthe slurry for reaction sintering, when the amount of amorphous carbonobtained from the resin is small, melt impregnation of silicon aftercarbonization can be performed. The second porous structural materialdescribed above corresponds to the case described above, and meltimpregnation of silicon is performed for a carbonized porous structuralbody which has carbon generated from the resin on the surface thereofand at the same time contains powdered carbon having a good wettabilityto molten silicon. Hence, when a slurry containing a resin used as acarbon source is applied by impregnation to a carbon powder-made porousstructural body having a bone structure, followed by carbonization, thecarbonized porous structural body is formed which has carbon generatedfrom the resin on the surface thereof and at the same time containspowdered carbon having a good wettability to molten silicon, and thiscarbonized porous structural body is then impregnated with moltensilicon. The other manufacturing conditions are the same as thosedescribed above.

EXAMPLES

Next, the methods of the present invention will be further described indetail with reference to examples; however, the present invention is notlimited thereto at all.

Example 1

A mixing ratio of a phenol resin to powdered silicon was set so that theratio of carbon formed from the phenol resin by carbonization to siliconon an atomic basis was 2 to 3, a slurry was prepared by dissolving thephenol resin in ethyl alcohol and was mixed using a ball mill for oneday in order to decrease diameters of particles of the powdered silicon,and an air conditioner filter having a laminated corrugated fiberboardshape made of powdered activated carbon was impregnated with the slurrythus prepared, followed by drying.

Next, this air conditioner filter was carbonized by firing in an argonatmosphere at 1,000° C. for one hour. The carbon-based porous body thusformed had a strength capable of sufficiently withstanding machining,and the shrinkage thereof was very small, such as approximately 3%. Bythe use of this carbon-based porous body, reaction sintering and meltimpregnation of silicon were performed at 1,450° C. for one hour in avacuum atmosphere, thereby obtaining a silicon carbide-basedheat-resistance porous composite material having a corrugated fiberboardshape.

The silicon carbide-based heat-resistance porous structural materialthus formed had the same structure as that of the corrugated fiberboardused as a starting material, the dimensions after carbonization were notchanged therefrom, and the surface was also flat. In addition, siliconcarbide-made bones had a large thickness and high strength as comparedto those obtained using a paper-made corrugated fiberboard.

Example 2

A slurry was prepared by dissolving a phenol resin in ethyl alcohol, andan air conditioner filter is impregnated with the slurry, followed bydrying, the filter having a laminated corrugated fiberboard shape madeof powdered active carbon. Next, this air conditioner filter wascarbonized by firing in an argon atmosphere at 1,000° C. for one hour.The carbon-based porous body thus formed had a strength capable ofsufficiently withstanding machining, and the shrinkage thereof was verysmall, such as approximately 3%. This carbon-based porous body wasprocessed by melt impregnation of silicon at 1,450° C. for one hour in avacuum atmosphere, thereby obtaining a silicon carbide-basedheat-resistance porous composite material having a corrugated fiberboardshape.

The silicon carbide-based heat-resistance porous structural materialthus formed had the same structure as that of the corrugated fiberboardused as a starting material, the dimensions after carbonization were notchanged therefrom, and the surface was also flat. In addition, siliconcarbide-made bones had a large thickness and high strength as comparedto those of a paper-made corrugated fiberboard.

Comparative Example 1

An air conditioner filter having a laminated corrugated fiberboard shapemade of powdered active carbon was carbonized by firing in an argonatmosphere at 1,000° C. for one hour. The carbon-based porous body thusformed was changed into powder when being touched with hands, and hencethe shape of the porous body cannot be maintained.

1. A silicon carbide-based heat-resistance porous structural materialproduced by a process comprising the step of: impregnating a carbonizedporous structural body with molten silicon, the structural body havingopen pores open to a surface thereof, which are generated due to avolume-reduction reaction, and at the same time containing poroussilicon carbide having a good wettability to molten silicon, wherein thecarbonized porous structural body is formed by the steps of applying aslurry by impregnation to a carbon powder-made porous structural bodyhaving a bone structure, which is formed from powdered carbon,carbonizing the slurry, and then performing reaction sintering, theslurry containing powdered silicon and a resin used as a carbon source.2. A silicon carbide-based heat-resistance porous structural materialproduced by a process comprising the step of: impregnating a carbonizedporous structural body with molten silicon, the structural body havingcarbon on a surface thereof generated from a resin and at the same timecontaining powdered carbon having a good wettability to molten silicon,wherein the carbonized porous structural body is formed by the steps ofapplying a slurry by impregnation to a carbon powder-made porousstructural body having a bone structure, which is formed from powderedcarbon, and then carbonizing the slurry.
 3. The silicon carbide-basedheat-resistance porous structural material according to claim 1 or 2,wherein, as the carbon powder-made porous structural body having a bonestructure, a carbon product having a honeycomb, a corrugated fiberboard,or a cardboard shape is used which is formed by adding a binding agentto the powdered carbon, followed by molding.
 4. A method formanufacturing a silicon carbide-based heat-resistance porous structuralmaterial, comprising the steps of: applying a slurry containing powderedsilicon and a resin used as a carbon source by impregnation to a carbonpowder-made porous structural body having a bone structure, which isformed from powdered carbon, then carbonizing the slurry at 900 to1,300° C. in a vacuum or an inert gas atmosphere, then performingreaction sintering at a temperature of 1,300° C. or more in a vacuum oran inert gas atmosphere so as to form a carbonized porous structuralbody having open pores which are generated by a volume-reductionreaction at the same time when porous silicon carbide having a goodwettability to molten silicon is formed, and impregnating thiscarbonized porous structural body with silicon at a temperature of 1,300to 1,800° C. in a vacuum or an inert gas atmosphere.
 5. A method formanufacturing a silicon carbide-based heat-resistance porous structuralmaterial, comprising the steps of: applying a slurry containing a resinused as a carbon source by impregnation to a carbon powder-made porousstructural body having a bone structure, which is formed from powderedcarbon, then carbonizing the slurry at 900 to 1,300° C. in a vacuum oran inert gas atmosphere so as to form a carbonized porous structuralbody having carbon generated on a surface thereof from the resin and atthe same time containing powdered carbon having a good wettability tomolten silicon, and impregnating this carbonized porous structural bodywith silicon at a temperature of 1,300 to 1,800° C. in a vacuum or aninert gas atmosphere.
 6. The method for manufacturing a siliconcarbide-based heat-resistance porous structural material, according toclaim 4 or 5, wherein, as the carbon powder-made porous structural bodyhaving a bone structure, a carbon product is used which is formed byextrusion of powdered carbon added with a binding agent into a honeycombshape or by paper making of powdered carbon added with a binding agentinto a corrugated fiberboard or a cardboard shape.
 7. The method formanufacturing a silicon carbide-based heat-resistance porous structuralmaterial, according to claim 4 or 5, wherein, as the resin applied byimpregnation to the bone structure of the carbon powder-made porousstructural body, at least one selected from the group consisting of aphenol resin, a furan resin, a polycarboxysilane, an organic metalpolymer, and pitch is used.
 8. The method for manufacturing a siliconcarbide-based heat-resistance porous structural material, according toclaim 4 or 5, wherein, as an additive added to the slurry with which thebone structure of the carbon powder-made porous structural body isimpregnated, at least one selected from the group consisting of powderedcarbon, powdered graphite, and carbon black is used.
 9. The method formanufacturing a silicon carbide-based heat-resistance porous structuralmaterial, according to claim 4 or 5, wherein, as an aggregate or anantioxidant added to the slurry with which the bone structure of thecarbon powder-made porous structural body is impregnated, at least oneselected from the group consisting of silicon carbide, silicon nitride,titania, zirconia, zircon, alumina, silica, mullite, molybdenumdisilicide, boron carbide, boron, and powdered silicon is used.
 10. Themethod for manufacturing a silicon carbide-based heat-resistance porousstructural material, according to claim 4 or 5, wherein, as the powderedsilicon contained in the slurry or the silicon used for meltimpregnation, a silicon alloy containing at least one element selectedfrom the group consisting of magnesium, aluminum, titanium, chromium,manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium,molybdenum, and tungsten, or a mixture of the above element and powderedsilicon is used.
 11. The method for manufacturing a siliconcarbide-based heat-resistance porous structural material, according toclaim 4 or 5, wherein, as the resin of the slurry applied byimpregnation to the bone structure of the carbon powder-made porousstructural body, at least one selected from the group consisting of aphenol resin, a furan resin, a polycarboxysilane, an organic metalpolymer, and pitch is used, and as an additive added to the slurry, atleast one selected from the group consisting of powdered carbon,powdered graphite, and carbon black is used.
 12. The method formanufacturing a silicon carbide-based heat-resistance porous structuralmaterial, according to claim 4 or 5, wherein, as an aggregate or anantioxidant added to the slurry applied by impregnation to the bonestructure of the carbon powder-made porous structural body, at least oneselected from the group consisting of silicon carbide, silicon nitride,titania, zirconia, zircon, alumina, silica, mullite, molybdenumdisilicide, boron carbide, boron, and powdered silicon is used, and asthe powdered silicon contained in the slurry or the silicon used formelt impregnation, a silicon alloy containing at least one elementselected from the group consisting of magnesium, aluminum, titanium,chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium,niobium, molybdenum, and tungsten, or a mixture of the above element andpowdered silicon is used.